Turning right to help Market Street

San Francisco may be known for its left-leaning politics, but it’s expanding its experiment to depend on right turns to help improve Market Street.

Beginning Tuesday, drivers behind the wheel of personal vehicles tooling eastbound on Market Street will be forced to turn right on 10th Street — two blocks farther west.

Since Sept. 29, the Municipal Transportation Agency has forced drivers to turn right on Eighth and Sixth streets as part of an experiment to see if the city can make the busy traffic corridor safer for pedestrians and bicyclists and less congested for the 12 Muni lines that cruise down Market.

After six weeks, the agency found, the average hourly traffic volume on Market east of Eighth Street decreased 54 percent. Further down Market, at Montgomery Street, after private cars are allowed onto the thoroughfare, the drop was just 5 percent. The impact on surrounding streets included a 15 percent rise in traffic on Mission Street, but Folsom Street saw increases and decreases.

Eastbound Muni buses experienced about a 50-second time savings on Market Street, and the percent of traffic comprised of bicyclists rose by about 15 percent.

The agency decided to extend the traffic diversion back two blocks because cars turning right from the center lane at Eighth Street endangered bike riders. Agency officials won’t say how long the experiment — a pet project of Mayor Gavin Newsom — will continue.